1. Field
The invention relates to cutting inserts used in cutting operations, particularly indexable cutting inserts for mining applications. The illustrated embodiment of the invention is an indexable cutting insert for chain saws used in the quarrying of natural stone.
2. State of the Art
Tools used in natural stone quarries for the cutting of stone have generally been known for many years. Traditionally, stone has been cut by large channel machines and wire saws in commercial stone quarry operations. Approximately two decades ago, large carriage mounted chain saws which ride on tracks were introduced into stone quarries. The basic component of the stone quarry chain saw are a power unit, such as an electric, gas or hydraulic motor, which rotates a hardened steel chain around an arm. The hardened steel chain has cutter links interposed along its length which house cutting inserts.
Typically, the cutting insert is brazed to a holder which is attached to the cutter link. When the cutting insert becomes dull, broken or fractured, the cutting insert can be debrazed from the holder and replaced by brazing a new cutting insert to the holder, or the cutter link is removable from the chain saw chain so that the cutter link and attached holder and cutting insert can be replaced, or, if the wearing or damage is extensive, the entire chain saw chain can be replaced. The cutting inserts are usually grouped in sets along the chain, each set comprising a multiplicity of cutting inserts having an increasing kerf width.
These prior art chain saw cutting insert arrangements are relatively expensive to maintain and operate. When the cutting inserts need replacement, it necessitates the shutting down of the chain saw and quarrying operation for an extended period of time to replace the cutting inserts by the above stated methods. Also required for maintenance is an extensive inventory of cutting inserts of varying kerf width so that the appropriate cutting insert which has become dull, broken or fractured can be replaced. To minimize down time, inventories of entire chain saw chains are often maintained so that an entire chain can be replaced.
It is well known in the prior art to use carbide or tungsten carbide cutting inserts. However, carbide or tungsten carbide cutting inserts have been primarily useful in quarrying limestone, marble, slate and travertine, and have been found unsuitable for abrasive stone such as sandstone and some highly abrasive limestone. The highly abrasive materials cause excessive wearing of the carbide or tungsten carbide cutting insert, thereby resulting in short tool life and excessive down time in the quarrying operation for cutting insert replacement.
In recent years new materials have been developed which replace the carbide or tungsten carbide or at least the cutting surface of mining and drilling tools. Through the use of high pressure, high temperature technology, superabrasive materials such as polycrystaline diamond compacts, commonly known as "PDC," and polycrystaline cubic boron nitride compacts, known and sold by General Electric Company under the trademark "BZN.RTM. Compacts," have been produced for use as the cutting surfaces in drilling and mining tools. PDC materials which are useful for these purposes are disclosed in U.S. Pat. No. 32,380 which teaches a PDC material which is sold by General Electric Company under the trademark STRATAPAX.RTM., U.S. Pat. No. 4,224,380 which teaches a thermally stable PDC, and U.S. Pat. No. 4,738,689 which teaches a coated thermally stable PDC, the latter materials being sold by General Electric Company under the trademark GEOSET.RTM.. BZN.RTM. Compacts are disclosed in U.S. Pat. Nos. 3,767,371 and 3,743,489. The foregoing General Electric Company patents are assigned to the same assignee as the present invention, and are incorporated herein by this reference.
In the prior art the superabrasive material is typically formed in a thin section having a narrow dimension and a broad dimension. The cutting surface is usually the surface along the broad dimension. The superabrasive material is typically bonded to a metallic substrate, with the metallic substrate oriented to support the cutting surface and minimize stress on the metallic substrate-superabrasive material joint.
In prior art chain saw cutting inserts, the superabrasive material is usually backed by and bonded to a metallic substrate which is manufactured of a harder material than the hardened steel of the cutter links. If the superabrasive material is bonded to the metallic substrate in the manufacturing process, the metallic substrate is then brazed to a carrier which is secured to the cutter link. Alternatively, the superabrasive material may be brazed to a carrier which is secured to the cutter link. The metallic substrate or the carrier is typically oriented to provide mechanical support for the superabrasive material to reduce fracturing thereof and to reduce stress on the superabrasive material-metallic substrate bond or superabrasive material-carrier braze joint. Metallic substrate materials which have been used in the past are carbide or a hard cemented metal such as cemented carbide. The prior art superabrasive material cutting inserts are also typically arranged in sets of increasing kerf widths. This also requires an inventory of superabrasive material cutter inserts of various widths to maintain the chain saw.
Square PDC blanks have been used as cutting inserts for chain saws in the prior art. Each of the corners of the PDC blank is a cutting surface. The PDC blank is brazed to a holder which is attached to the cutter link of the chain saw chain. After one corner of the PDC blank becomes worn, the PDC blank is debrazed from the holder, rotated ninety degrees and rebrazed to the holder. This operation is repeated until all four corners of one side of the PDC blank have been used as cutting surfaces. The PDC blank is then rotated one hundred eighty degrees to the opposite side and this process repeated. In this process, the PDC blank is repeatedly subjected to elevated temperatures and potential thermal damage. Since only the corners of the PDC blank are used as cutting surfaces, the remaining portions of the PDC blank is waste material.